PSI - Issue 20

Yakovleva S. P. et al. / Procedia Structural Integrity 20 (2019) 154–160 Yakovleva S. P. et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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2. Study object, procedure and methods The study object was the standard master spring leaf of front suspension of the KAMAZ truck after a fatigue breakdown by Yakovleva et al. (2017). The spring was 1675x75x10 mm in size. The fatigue breakdown occurred at a stage corresponding to normal wear of the spring. The crack propagated at about 170 mm from a front end of the spring and split it into a short fragment and long one. Fig. 1. shows the destroyed half of the spring. For the study structure and microscale mechanical properties and subsequent determination of the impact toughness, the long fragment was used to fabricate three groups of 10x10x55 mm longitudinal Charpy specimens that corresponded to spring zones I, II, and III with the various degrees of the damage (the most loaded areas are spots of clamping the springs to an axle and frame of the truck). For the study of the damage, the parameters of the microhardness (for a description of the microdamage) and porosity (for the description of the mesoscale damage) were used, i.e., two types of the structural damage different in the scale were distinguished by Volegov et al. (2015), Zorin et al. (2009). The microhardness Н 100 was measured on a PMT-3 instrument with the indenter load of 0.98 N (100 g.wt.). A sample volume for each zone of the spring was about 1000 indents. The statistical analysis was conducted in Excel. In addition, a structural microdamage accumulation coefficient k was found for the specimens from all three groups by the procedure described in by Zorin (2013) and using an array of the values of Н 100 .

Fig. 1. General view of the fragments of a destroyed spring and their schematic view; the dashed line indicates the orientation of the specimens cut out from zones I, II, and III with various load levels Pore characteristics were determined on three 2x1.4 mm 2 areas observed under a Neophot-32 optic microscope. According to their cross section, the pores were tentatively divided into fine (up to 20 μ m ) and coarse (the largest of the observed pores did not exceed 40 μ m in size); volume fractions of the fine and coarse pores are indicated as V fine and V crs , respectively, whereas the total porosity is indicated as V total . The impact-bending tests of the Charpy specimens were conducted at 20, – 20, and – 60 о C on an Amsler RKP 450 Zwick pendulum impact testing machine. 3. Main results and discussion 3.1. Impact of seasonal changes in air temperature and road profile on working capacity of KAMAZ truck springs in the North The significant seasonal changes in the temperature and load conditions of the operation in the cryolithozone affect the working capacity of the vehicles. The impact of the road conditions on the parts and systems of the vehicle, which limit the car reliability, can be seen in the graphs of the failure distribution of these elements by the months of the year. The carried out studies have shown that the external air temperatures and road conditions determine the failure of the suspension elements to the greatest extent. This is mainly due to dependence of the dynamic loads on the evenness of the roads. Formation of the longitudinal and transverse profile of the roads that do not have the hard surface depends primarily on the climatic conditions of a region. Thus, the bearing capacity of dirt